Question

A thin circular ring M and radius ‘r’ is rotating about its axis with a constant angular velocity ω. Four objects each of mass m, are kept gently to the opposite ends of two perpendicular diameters of the ring. The angular velocity of the ring will be -

• A. $\frac {Mω}{4m}$
• B. $\frac {Mω}{M+4m}$
• C. $\frac {(M+4m)ω}{M}$
• D. $\frac {(M+4m)ω}{M+4m}$

Answer 1

Answer: (B)

$\frac {Mω}{M+4m}$

Answer 2

Use law of conservation of angular momentum.
$Mr^2ω = (Mr^2+4mr^2)ω'$
$⇒ω'=\frac {Mω}{M+4m}$

So, the correct option is (B): $\frac {Mω}{M+4m}$